1. Technical Field
The present invention relates to a control apparatus for a vehicle. Particularly, the present invention relates to measures to provide a suitable driving force to a vehicle equipped with a CVT (continuously variable transmission).
2. Related Art
Vehicles are already known in which an automatic transmission is incorporated into a power train for transmitting power from a drive power source, such as an engine (internal combustion engine), toward drive wheels. In such a vehicle, upon change of the vehicle speed or the like, the gear ratio of the automatic transmission is changed according to a previously stored shift map (see, for example, JP-A No. 2012-107537).
JP-A No. 2007-177966 discloses a technique in which the gear ratio of the automatic transmission of a vehicle while slowing down (decelerating) is determined based on the deceleration of the decelerating vehicle. Specifically, a shift determination region is previously set in a graph with the lateral acceleration and longitudinal acceleration of the vehicle as variables. In the shift determination region, an upshift prohibited zone and a downshift zone are previously defined. The shift determination region contains shift determination values set based on synthetic accelerations each given by a lateral acceleration and a longitudinal acceleration of the decelerating vehicle. If the shift determination value is within the upshift prohibited zone of the determination region (for example, if the vehicle is turning and its lateral acceleration reaches or exceeds a predetermined value), an upshift to the gear ratio obtained from a shift map is prohibited. Thus, the re-accelerability can be ensured. On the other hand, if the shift determination value is within the downshift zone of the determination region (for example, if the vehicle is rapidly slowing down while moving straight and its lateral acceleration is below the predetermined value), a downshift according to the shift map is executed. Thus, the deceleration is increased.
It is preferred that when the vehicle exits corners after turning around them (it transitions from the travel on a curved path to the travel on a straight path), the gear ratio of the automatic transmission should offer a driving force meeting the driver's intention of re-acceleration (a target driving force at re-acceleration). More specifically, even at the same synthetic acceleration during deceleration, the driver's intention of re-acceleration in each case may be different depending upon his/her intention of deceleration (for example, the manner of deceleration). Therefore, gear ratios should preferably be previously set to offer a driving force suitable for the driver's intention of re-acceleration in each case.
In the technique disclosed in JP-A No. 2007-177966, the gear ratio is simply set based on the synthetic acceleration of the decelerating vehicle. In this instance, a driving force suitable for the driver's intention of re-acceleration in each case may not be able to be offered. For example, if a gear ratio not meeting a target driving force at re-acceleration has been set (if a preset gear ratio is below an appropriate value), it is necessary to execute a shift control toward increasing the gear ratio (downshift) by depressing an accelerator pedal at re-acceleration. In doing so, the acceleration response during re-acceleration may not be able to be sufficiently achieved. On the other hand, if a preset gear ratio is above the gear ratio suitable for meeting the target driving force at re-acceleration, the driver may be given a feeling of strangeness from an unexpected response during re-acceleration.